Methods and systems for exhalation control and trajectory optimization

ABSTRACT

This disclosure describes systems and methods for controlling pressure and/or flow during exhalation. The disclosure describes novel exhalation modes for ventilating a patient.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation application of U.S. patentapplication Ser. No. 15/456,892, entitled “METHODS AND SYSTEMS FOREXHALATION CONTROL AND TRAJECTORY OPTIMIZATION,” filed on Mar. 13, 2017,which is a continuation application of U.S. patent application Ser. No.13/098,130, entitled “METHODS AND SYSTEMS FOR EXHALATION CONTROL ANDTRAJECTORY OPTIMIZATION,” filed Apr. 29, 2011, the disclosures of whichare hereby incorporated herein by reference.

INTRODUCTION

Medical ventilator systems have long been used to provide supplementaloxygen support to patients. These ventilators typically comprise asource of pressurized air and oxygen, and which is fluidly connected tothe patient through a conduit or tubing. The amount of pressure in thegas mixture delivered to the patient may be controlled duringventilation including during inspiration and exhalation.

Patients on a ventilator system are more comfortable when the deliveredvolume of inspired gas is allowed to be exhaled in the shortest amountof time possible. Current exhalation modes are designed to reducepressure in the tubing as fast as possible. Other exhalation modesreduce the pressure in the patient tubing to a preset positiveend-expiratory pressure (PEEP) level as fast as possible and thenmaintain this PEEP level through the remainder of the exhalation period.These exhalation modes are based on the assumption that achieving thehighest pressure gradient across the flow restriction promotes thegreatest lung flow at any point in time, and the fastest rate of lungemptying.

SUMMARY

This disclosure describes systems and methods for controlling pressureand/or flow during exhalation. The disclosure describes novel exhalationmodes for ventilating a patient.

In part, this disclosure describes a method for controlling exhalationduring ventilation of a patient on a ventilator. The method includes:

a) determining at least one determined pressure profile based on atleast one received criterion for an exhalation by a patient beingventilated on a ventilator;

b) selecting a pressure profile for delivery to the patient from the atleast one determined pressure profile; and

c) controlling at least one of airway pressure and flow based on theselected pressure profile during the exhalation by the patient.

Yet another aspect of this disclosure describes a method for optimizinga pressure profile delivered to a patient during exhalation on aventilator including:

a) delivering at least one of airway pressure and flow based on apressure profile during a current exhalation to a patient duringventilation on a ventilator;

b) monitoring at least one parameter during the current exhalation bythe patient;

c) modifying the pressure profile based at least in part on themonitored at least one parameter; and

d) delivering at least one of a modified airway pressure and a modifiedflow based on the modified pressure profile to the patient during atleast one of the current exhalation and the next exhalation.

Further, the modified pressure profile maintains a received PEEP.

The disclosure further describes a computer-readable medium havingcomputer-executable instructions for performing a method controllingexhalation during ventilation of a patient on a ventilator. The methodincludes:

a) repeatedly determining at least one determined pressure profile basedon at least one received criterion for an exhalation by a patient beingventilated on a ventilator;

b) repeatedly selecting a pressure profile for delivery to the patientfrom the at least one determined pressure profile; and

c) repeatedly controlling at least one of airway pressure and flow basedon the selected pressure profile during the exhalation by the patient.

The disclosure also describes a ventilator system including means fordetermining at least one determined pressure profile based on at leastone received criterion for an exhalation by a patient being ventilatedon a ventilator; means for selecting a pressure profile for delivery tothe patient from the at least one determined pressure profile; and meansfor controlling at least one of airway pressure and flow based on theselected pressure profile during the exhalation by the patient.

The disclosure further describes a ventilator system including means fordelivering at least one of airway pressure and flow based on a pressureprofile during a current exhalation to a patient during ventilation on aventilator; means for monitoring at least one parameter during thecurrent exhalation by the patient; means for modifying the pressureprofile based at least in part on the monitored at least one parameter;and means for delivering at least one of a modified airway pressure anda modified flow based on the modified pressure profile to the patientduring at least one of the current exhalation and the next exhalation.Further, the modified pressure profile maintains a received PEEP.

These and various other features as well as advantages whichcharacterize the systems and methods described herein will be apparentfrom a reading of the following detailed description and a review of theassociated drawings. Additional features are set forth in thedescription which follows, and in part will be apparent from thedescription, or may be learned by practice of the technology. Thebenefits and features of the technology will be realized and attained bythe structure particularly pointed out in the written description andclaims hereof as well as the appended drawings.

It is to be understood that both the foregoing general description andthe following detailed description are exemplary and explanatory and areintended to provide further explanation of the invention as claimed.

EXHALATION CONTROL AND TRAJECTORY OPTIMIZATION

The following drawing figures, which form a part of this application,are illustrative of embodiments, systems and methods described below andare not meant to limit the scope of the invention in any manner, whichscope shall be based on the claims appended hereto.

FIG. 1 illustrates an embodiment of a ventilator.

FIG. 2 illustrates an embodiment of an exhalation module.

FIG. 3 illustrates an embodiment of a schematic model of a lungdemonstrating the pressure and resistance relationship within the twocompartments of the lung.

FIG. 4 illustrates an embodiment of a pressure profile.

FIG. 5 illustrates an embodiment of a method for controlling exhalationduring ventilation of a patient on a ventilator.

FIG. 6 illustrates an embodiment of a method for optimizing exhalationduring ventilation of a patient on a ventilator.

FIG. 7 illustrates an embodiment of a graph of the effect of differentpatient's tubing exhalation pressure profiles on the time required topassively exhale 50% of a given inspired tidal volume in simulations

FIG. 8 illustrates an embodiment of a graph of the effect of differentpatient's tubing exhalation pressure profiles on the time required topassively exhale 90% of a given inspired tidal volume in simulations.

DETAILED DESCRIPTION

Although the techniques introduced above and discussed in detail belowmay be implemented for a variety of medical devices, the presentdisclosure will discuss the implementation of these techniques in thecontext of a medical ventilator for use in providing ventilation supportto a human patient. The reader will understand that the technologydescribed in the context of a medical ventilator for human patientscould be adapted for use with other systems such as ventilators fornon-human patients and general gas transport systems.

Medical ventilators are used to provide a breathing gas to a patient whomay otherwise be unable to breathe sufficiently. In modern medicalfacilities, pressurized air and oxygen sources are often available fromwall outlets. Accordingly, ventilators may provide pressure regulatingvalves (or regulators) connected to centralized sources of pressurizedair and pressurized oxygen. The regulating valves function to regulateflow so that respiratory gas having a desired concentration of oxygen issupplied to the patient at desired pressures and rates. Ventilatorscapable of operating independently of external sources of pressurizedair are also available.

While operating a ventilator, it is desirable to control the percentageof oxygen in the gas supplied by the ventilator to the patient. Further,it is desirable to control the amount of pressure delivered to thepatient during inspiration. In some ventilators, it is desirable tocontrol the amount of pressure delivered to the patient duringexhalation.

The pressure control provided during exhalation is based on theassumption that patients find it more comfortable to exhale unimpeded.For example, modes of exhalation have been designed to reduce thepressure in the patient tubing to a preset positive end exhalationpressure (PEEP) level or to atmospheric pressure as fast as possible. Ifa preset PEEP is utilized, the exhalation mode must also maintain thispressure at the set PEEP level throughout exhalation. This exhalationapproach is justified by the belief that achieving the highest pressuregradient across the flow restriction promotes the greatest lung flow atany point in time, and the fastest rate of lung emptying. This approachis correct if the resistance of the airways is independent from theactual pressure in the airways and lungs.

However, the resistance of lung airways may not always be independentfrom the actual pressure in the airways and lungs. It is suspected thata nonlinear character of resistance of internal lung airways causes theexhalation lung flow to decay more rapidly than normal therebypreventing complete lung emptying, causing patients discomfort,suboptimal ventilation, etc. For example, the physiology of the lung andairways associated with different disease states has been identified asa significant contributor to the impairment of the normal lung emptyingprocess during exhalation. Thus, this nonlinear dependency of theairways resistance to the lung and airway pressure may result in anon-intuitive relationship between the optimum tubing pressure profileand the exhalation lung flow. Accordingly, it is desirable to modify theexhalation mode to obtain a faster rate of lung emptying or to decreasethe amount of time it takes the patient to passively expire an inspiredvolume of gas to provide for faster and/or complete lung emptying.

FIG. 1 is a diagram illustrating an embodiment of an exemplaryventilator 100 connected to a human patient 150. Ventilator 100 includesa pneumatic system 102 (also referred to as a pressure generating system102) for circulating breathing gases to and from patient 150 via theventilation tubing system 130, which couples the patient 150 to thepneumatic system 102 via an invasive (e.g., endotracheal tube, as shown)or a non-invasive (e.g., nasal mask) patient interface 180.

Ventilation tubing system 130 (or patient circuit 130) may be a two-limb(shown) or a one-limb circuit for carrying gases to and from the patient150. In a two-limb embodiment, a fitting, typically referred to as a“wye-fitting” 170, may be provided to couple a patient interface 180 (asshown, an endotracheal tube) to an inspiratory limb 132 and anexpiratory limb 134 of the ventilation tubing system 130.

Pneumatic system 102 may be configured in a variety of ways. In thepresent example, pneumatic system 102 includes an expiratory module 108coupled with the expiratory limb 134 and an inspiratory module 104coupled with the inspiratory limb 132. Compressor 106 or other source(s)of pressurized gases (e.g., air, oxygen, and/or helium) is coupled withinspiratory module 104 and the expiratory module 108 to provide a gassource for ventilatory support via inspiratory limb 132.

The inspiratory module 104 determines the pressure profiles deliveredduring inspiration. The expiratory module 108 determines the pressureprofiles delivered during exhalation. In one embodiment, the inspiratorymodule 104 and the expiratory module 108 determine the pressure profilesduring ventilation by controlling valves and gas flow within theventilator 100. As used herein, the term “pressure profile” refers tohow pressure is delivered for the entire period of exhalation, such asthe amount of pressure per second or millisecond of the exhalation timeperiod. In an alternative embodiment, the inspiratory module 104 and theexpiratory module 108 determine the pressure profiles during ventilationby sending instructions to the controller 110 to control the valves andgas flow within the ventilator 100 during ventilation.

Previously utilized systems provided pressure control during exhalationbased on the assumption that patients find it more comfortable to exhalefast and on the belief that achieving the highest pressure gradientacross the flow restriction promotes the greatest lung flow at any pointin time, and the fastest rate of lung emptying. This previously utilizedapproach is correct if the resistance of the airways is independent fromthe actual pressure in the airways and lungs. However, the resistance oflung airways may not always be independent from the actual pressure inthe airways and lungs. It is suspected that a nonlinear character ofresistance of internal lung airways causes the exhalation lung flow todecay more rapidly than normal thereby preventing complete lungemptying, causing patients discomfort, suboptimal ventilation, etc.

Accordingly, the expiratory module 108 determines the pressure profiledelivered during exhalation based on at least one received criterion.The at least one received criterion does not include a received or setPEEP. However, the pressure profile determined by the expiratory module108 may include a received or a set PEEP in addition to the received atleast one criterion.

For the example, the at least one criterion may include a nonlinearrelationship between airway resistance and the lung and airway pressurewithin a patient. A relationship between the airway resistance to lungand airway pressure exists because the lungs are essentially dividedinto two compartments: 1) the upper airways; and 2) the lower airways.These two compartments of the lung create a relationship, which isnonlinear, between airway resistance and lung and airway pressure. Inone embodiment, this nonlinear relationship is modeled by the followingequation:R _(L) =f(P _(L1) ,P _(L2)).

In the above equation R_(L) is the amount of resistance in the lungs,f(⋅) is a nonlinear function of two values, P_(L1) and P_(L2), where,P_(L1) is the amount of pressure in the first compartment of the lungs,and P_(L2) is the amount of pressure in the second compartment of thelungs. As would be known by a person of skill in the art, the abovenonlinear equation may be a function of more than two values. FIG. 3illustrates this model by showing the pressure and resistancerelationships between the upper airways or lung compartment 1 (C_(L1)),the lower airways or lung compartment 2 (C_(L2)), and the trachea. FIG.3 also illustrates the flow (q_(L)) within the lungs and the externalpositive pressure (P_(p)) acting upon the lungs. Further, the physiologyof the lung and airways associated with different disease states may bea significant contributor to the impairment of the normal lung emptyingprocess. Accordingly, a pressure profile taking into account a nonlinearrelationship, such as the example nonlinear relationship shown above,may provide for more comfortable and faster exhalation for somepatients.

The nonlinear relationship of the lung illustrated above is just oneexample of a non-linear pressure flow relationship that may exist in apatient. Other nonlinear relationships, between airway resistance andlung and airway pressures may exist within a patient and vary betweenpatients based on their measured parameters and diseases. For, example,the resistance can be a nonlinear function of more than two differentlocal pressures measured in different parts of the lung and airways.Further, not all patients exhibit a measureable nonlinear relationshipbetween airway resistance and lung and airway pressure. Accordingly, theexpiratory module 108 determines the pressure profile to deliver duringexhalation based on at least one received criterion, such as ventilatordata, predetermined nonlinear pressure profiles, pressure profiletrajectory equations, operator determined pressure profiles, and/ormeasured, derived, inputted, and/or selected patient parameters todetermine how to provide a pressure profile with the fastest rate oflung emptying. As discussed above, the at least one criterion does notinclude a received/set PEEP. However, the at least one criterion may beany suitable criterion for controlling or effecting the pressure profileto provide for a faster rate of lung emptying, such as a percent ofinspired volume/elapsed time, a flow as a function of delta P (estimatedlung pressure and circuit pressure), an AutoPEEP, measurements ofpatient resistance and/or compliance, a diagnosis (e.g., chronicobstructive pulmonary disease), an inner diameter of artificial airway,a type of patient interface (e.g., mask or tube), an ideal body weight,carbon dioxide levels in exhaled gas and/or blood, an end expiratoryflow, a patient assessment of comfort/dyspnea, a percentage of volumeexhaled within a given period of time after the start of exhalation, amean expiratory flow, a peak expiratory flow, a time to exhale apredetermined percentage of inspired volume, a time to reach apredetermined level of expiratory flow, a functional residual capacity(FRC), a ratio of functional residual capacity to total lung capacity(FRC/TLC), a breath rate, a ratio of inspiratory to expiratory time, atidal volume, a forced expiratory volume in 1 second (FEV₁), anexpiratory lung volume, and/or an instantaneous level of flow.

As used herein, any parameters/criteria that are “received” are input bythe clinician, selected by the clinician, or provided by the ventilator.The ventilator may derive the “received” parameter/criteria based onpatient parameters, ventilator parameters, and/or input or selectedclinician data. In some embodiments, the ventilator contains storeddefault values that are “received” or utilized by the ventilator whenthe clinician does not input or select a parameter or a criterion. Asused herein, the term “predetermined” designates that a value was set bya clinician and/or determined by the ventilator prior to use of thevalue.

The pneumatic system 102 may include a variety of other components,including mixing modules, valves, sensors, tubing, accumulators,filters, etc. Controller 110 is operatively coupled with pneumaticsystem 102, signal measurement and acquisition systems, and an operatorinterface 120 that may enable an operator to interact with theventilator 100 (e.g., change ventilator settings, select operationalmodes, view monitored parameters, etc.). Controller 110 may includememory 112, one or more processors 116, storage 114, and/or othercomponents of the type commonly found in command and control computingdevices. In the depicted example, operator interface 120 includes adisplay 122 that may be touch-sensitive and/or voice-activated, enablingthe display 122 to serve both as an input and output device.

The memory 112 includes non-transitory, computer-readable storage mediathat stores software that is executed by the processor 116 and whichcontrols the operation of the ventilator 100. In an embodiment, thememory 112 includes one or more solid-state storage devices such asflash memory chips. In an alternative embodiment, the memory 112 may bemass storage connected to the processor 116 through a mass storagecontroller (not shown) and a communications bus (not shown). Althoughthe description of computer-readable media contained herein refers to asolid-state storage, it should be appreciated by those skilled in theart that computer-readable storage media can be any available media thatcan be accessed by the processor 116. That is, computer-readable storagemedia includes non-transitory, volatile and non-volatile, removable andnon-removable media implemented in any method or technology for storageof information such as computer-readable instructions, data structures,program modules or other data. For example, computer-readable storagemedia includes RAM, ROM, EPROM, EEPROM, flash memory or other solidstate memory technology, CD-ROM, DVD, or other optical storage, magneticcassettes, magnetic tape, magnetic disk storage or other magneticstorage devices, or any other medium which can be used to store thedesired information and which can be accessed by the computer.

FIG. 2 illustrates an exhalation module 200. The exhalation module 200may include memory, one or more processors, storage, and/or othercomponents of the type commonly found in command and control computingdevices as described above. The exhalation module 200 further includes apressure profile module 202 and a parameters module 204.

The pressure profile module 202 determines the pressure profiledelivered during exhalation based on at least one received criterion.This pressure profile affects the amount of time a patient takes toexhale the inspired amount of inspiratory gas and rate of lung emptying.

The pressure profile module 202 utilizes at least one criterion forreducing the amount of time it takes the patient to exhale an inspiredvolume of gas and/or for increasing the rate of lung emptying as wouldbe known by a person of skill in the art. As discussed above, the atleast one criterion does not include a received PEEP. However, thepressure profile module 202 may utilize a received PEEP in addition tothe received at least one criterion for determining the pressureprofile. The at least one criterion may include ventilator data,predetermined pressure profiles, pressure profile trajectory equations,operator determined pressure profiles, a nonlinear relationship betweenairway resistance to the lung and airway pressure, and/or measured,derived, inputted, and/or selected patient parameters.

For example, the at least one criterion may include patient parameters,such as height, heart rate, weight, diseases, ideal body weight, etc.The criterion may further include ventilator data, such as flow rate,respiration rate, ventilation modes, expiration time, etc. The pressureprofile module 202 may receive the at least one criteria from otherventilator components (e.g., a sensor, user interface, and/orcontroller) and/or may calculate/derive the desired criteria fromreceived criteria or parameters. The ventilator may determine thedesired pressure profile for each breath, over a fixed number of breaths(e.g., take data over a fixed number of breaths), or for a predeterminedperiod of time. Further, the ventilator may repeat this calculationperiodically as determined by a ventilator or as selected by theoperator.

In some embodiments, the at least one criterion is ventilator data orpatient parameters, such as a current ventilation mode and/or adiagnosed patient condition. In other embodiments, the criterion is agroup of pressure profiles provided by the ventilator, which theoperator may select the pressure profile from. Any suitable pressureprofile for shortening the amount of time to exhale the delivered amountof inspiratory gas or for increasing the rate of lung emptying based onthe at least one received criterion may be utilized by the exhalationmodule 200.

In one embodiment, the at least one criterion includes an exhalationpressure fall time parameter (EPFTP). The EPFTP is the amount of time ittakes for the pressure to drop from the inspiratory pressure level tothe set PEEP level during exhalation. In one embodiment, the actual rateof pressure decay in the ventilator is defined by the EPFTP. In anotherembodiment, the pressure profile module 202 determines the pressureprofile based on the actual rate of pressure decay as defined by theEPFTP.

In a further embodiment, pressure profile module 202 determines thepressure profile based on the at least one criterion of an actual rateof pressure decay in the ventilator 100 as defined by predeterminedparameters that are settable and modified by operators or the ventilatorautomatically. In another embodiment, the at least one criterion is afamily of different pressure profiles that is utilized by the pressureprofile module 202 to determine the pressure profile. The family ofdifferent pressure profiles may be defined by a predetermined set ofcriteria, such as EPFTP and exhalation time.

In an additional embodiment, the pressure profile module 202 utilizes atleast one parameter that is repeatedly monitored during an exhalation tooptimize the pressure profile. In this embodiment, the pressure profileis adjusted or modified during the current exhalation and/or before thenext exhalation according to the monitored parameter in order to achievea smaller time required to exhale the delivered amount of inspiratorygas and/or to achieve a faster rate of lung emptying in the nextexhalation.

In another embodiment, the pressure profile module 202 utilizes repeatedmeasurements of the time required to exhale the delivered amount ofinspiratory gas to optimize the pressure profile. In this embodiment,different parameters of the pressure profile are adjusted after eachexhalation according to the measured time required to exhale thedelivered amount of inspiratory gas in order to achieve a shorter timerequired to exhale the delivered amount of inspiratory gas in the nextexhalation.

In one embodiment, the at least one criterion is the pressure at thepatient wye-fitting or the trajectory of the pressure profile. In someembodiments, the trajectory or the patient wye-fitting is determinedbased on the following equation:P _(y)=PEEP+(EIP−PEEP)e ^(−αt).

In this equation, P_(y) is the pressure at the patient wye-fitting, PEEPis the set positive end exhalation pressure, EIP is the measured endinspiratory pressure, α is greater than zero and denotes the EPFTP, andt is the amount of time measured from the onset of an exhalation phase.This equation illustrates an exponential decay from EIP to PEEP, withalpha being varied to create different trajectories. For example, alphamay be varied (e.g., 0.1, 0.2, 0.3, . . . ∞) and then optimized basedupon a predetermined parameter, such as the amount of time it takes thepatient to exhale 50% of an inspired volume.

In some embodiments, the at least one criterion utilized by the pressureprofile module is an operator-determined pressure profile. The operatormay select or input a desired pressure profile or input variousdifferent parameters for modifying a pressure profile as desired.Allowing the operator to adjust, change, and input a pressure profileprovides the operator with several benefits. For instance, the operatormay select a pressure profile based on patient comfort. For example, theoperator may deliver two different pressure profiles to a patient, askthe patient which profile the patient prefers, and then select apressure profile based on the patient's answer.

In other embodiments, the at least one criterion utilized by thepressure profile module is a nonlinear relationship between airwayresistance to the lung and airway pressure. In another embodiment, thepressure profile module 202 utilizes a predetermined nonlinear pressureprofile as the at least one criteria, such as a nonlinear pressureprofile with a fast initial decay in pressure followed by an increase ofpressure to provide a shorter amount of time required to exhale thedelivered amount of inspiratory gas. For example, an embodiment of apredetermined nonlinear pressure profile for the pressure profile module202 is illustrated in FIG. 4 . FIG. 4 illustrates a pressure profilewith a fast initial decay of pressure that actually drops below a setPEEP, then increases in pressure to above the set PEEP at time 0.50seconds followed by a gradual pressure reduction after the increase inpressure at time 0.8 seconds back down to the set PEEP.

The at least one criterion may be any suitable criterion for controllingor effecting the pressure profile to provide for a faster rate of lungemptying, such as a percent of inspired volume/elapsed time, a flow as afunction of delta P (estimated lung pressure and circuit pressure), anAutoPEEP, measurements of patient resistance and/or compliance, adiagnosis (e.g., chronic obstructive pulmonary disease), an innerdiameter of artificial airway, a type of patient interface (e.g., maskor tube), an ideal body weight, carbon dioxide levels in exhaled gasand/or blood, an end expiratory flow, a patient assessment ofcomfort/dyspnea, a percentage of volume exhaled within a given period oftime after the start of exhalation, a mean expiratory flow, a peakexpiratory flow, a time to exhale a predetermined percentage of inspiredvolume, a time to reach a predetermined level of expiratory flow, afunctional residual capacity (FRC), a ratio of functional residualcapacity to total lung capacity (FRC/TLC), a breath rate, a ratio ofinspiratory to expiratory time, a tidal volume, a forced expiratoryvolume in 1 second (FEV₁), an expiratory lung volume, and/or aninstantaneous level of flow.

The embodiments for determining the pressure profiles by the pressureprofile module 202 as described and discussed above are exemplary onlyand may be utilized alone or in various combinations. It is understoodby a person of skill in the art that any suitable pressure profile basedon the received PEEP and the at least one received criterion may beutilized by the pressure profile module 202.

In some embodiments, if more than one pressure profile is determined bythe pressure profile module 202, then the pressure profile module 202selects the pressure profile with the fastest rate lung emptying to besent to the parameters module 204. Further, the pressure profile modulemay present some or all of the unselected pressure profiles to theoperator for selection depending on how the system is implemented andthe degree of operator control desired. In a further embodiment, if morethan one pressure profile is determined by the pressure profile module202, then the pressure profile module 202 presents all of the pressureprofiles to the operator for selection and continues to deliver thepreviously utilized pressure profile during exhalation until a newpressure profile is selected by the operator.

The ventilator may utilize various different methods to determinedifferent pressure profiles. For example, the ventilator may utilizedifferent criteria to determine different pressure profiles. In thisembodiment, the ventilator may automatically select the pressure profilecalculated with a specific criterion, such as a measurement of patientcompliance and/or resistance, and only utilize the other calculatedpressure profiles based on other criterion if a predetermined thresholdis met by other measured patient or ventilator parameters. If thethreshold is met, the ventilator may select a pressure profilecalculated based on exhalation time. In some embodiments, the ventilatormay have a predetermined nonlinear pressure profile stored, such as theone displayed in FIG. 4 , in addition to a calculated pressure profile.In this embodiment, the ventilator may automatically select thecalculated pressure profile unless a predetermined threshold is met bypatient or ventilator measured parameters. For example, thepredetermined threshold may be related to work of breathing or arterialblood gas saturation. The selection parameters listed above are merelyexemplary. The ventilator may utilize any suitable means for selecting apressure profile from a family of pressure profiles as would be known bya person of skill in the art for ventilating a patient.

In some embodiments, the family of pressure profiles is createdutilizing the following equation:P _(y)(t)=PEEP+(EIP−PEEP)e ^(−αt)which is described in detail above. In this embodiment, different valuesfor alpha ranging from 0.1 to 100 and/or to infinity may be applied overa time period to generate several different pressure profiles. Theventilator may select one of these calculated pressure profilesutilizing various different techniques. For example, the ventilator maycompare the calculated pressure profiles to previously deliveredpressure profiles and choose the calculated pressure profile closest toa previously utilized pressure profile that obtained the fastest rate oflung emptying. In another embodiment, the ventilator delivers adifferent calculated exhalation profile in each breath for at least twoconsecutive breaths. The ventilator in this scenario may then selectwhich pressure profile to deliver based on a predetermined parameter,such as the amount of time it takes the patient to exhale 50% of aninspired volume, which was measured during the delivery of the pressureprofile.

For example, a pressure profile with an alpha of 1 may be delivered in afirst breath and a pressure profile with an alpha of 2 may delivered ina second breath. During the delivery of these pressure profiles theventilator may measure the amount of time it takes a patient to exhale90% of the volume of an inspired breath. In this example, the ventilatorcompares each of these measured times and then delivers in the nextexhalation the pressure profile with the shortest measured time.

The parameters module 204 receives the pressure profile for the currentor next exhalation from the pressure profile module 202. The parametersmodule 204 determines the necessary ventilator settings for deliveringairway pressure and/or flow based on the received pressure profile. Inone embodiment, the parameters module 204 sends the necessary ventilatorsettings to a controller for implementation. In an alternativeembodiment, the parameters module 204 sends the instructions directly tothe necessary component or components (e.g., to the exhalation valve)for implementing the desired pressure profile during exhalation.

In some embodiments, the exhalation module 200 is part of the pressuregenerating system 102, as illustrated in FIG. 1 . In alternativeembodiments, the exhalation module 200 is part of the controller 110. Insome embodiments, the pressure profile module 202 and/or the parametersmodule 204 are separate from the exhalation module and are containedwithin the controller 110.

FIG. 5 illustrates an embodiment of a method 500 for controllingexhalation during ventilation of a patient on a ventilator. Asillustrated, method 500 includes a determination operation 502. Theventilator in determination operation 502 determines at least onepressure profile by utilizing at least one received criterion for anexhalation by a patient being ventilated on a ventilator.

The at least one received criterion includes ventilation data, anonlinear relationship between airway resistance and lung and airwaypressure, predetermined pressure profiles, operator designed pressureprofiles, pressure profile trajectory equations, and/or input, selected,measured, and/or derived patient parameters. As discussed above, thereceived criterion does not include a received PEEP. However, thedetermination operation 502 may utilize a received PEEP in addition tothe received at least one criterion to determine the pressure profile.In some embodiments, the at least one criterion includes a currentventilation mode and/or a diagnosed patient condition. In someembodiments, the at least one criterion is a monitored parameter, suchas a patient or ventilator parameter, from previous deliveredexhalations. For example, the measured at least one parameter may beobtained for each breath, over a period of more than one breath (e.g.,take data over a fixed number of breaths), or over a period of time. Anysuitable pressure profile for shortening the amount of time to exhalethe delivered amount of inspiratory gas and/or for increasing the rateof lung emptying may be utilized by the ventilator during method 500.

In one embodiment, the at least one criterion utilized by the ventilatorin the determination operation 502 to determine the pressure profile isan EPFTP. In another embodiment, the at least one criterion utilized bythe ventilator in the determination operation 502 to determine thepressure profile is the actual rate of pressure decay. The actual rateof pressure decay may be defined by the EPFTP. In a further embodiment,the at least one criterion utilized by the ventilator in thedetermination operation 502 to determine the pressure profile is theactual rate of pressure decay in the ventilator as defined bypredetermined parameters, which are settable and modified by operatorsor the ventilator automatically. The parameters may be predetermined andmay include the set PEEP and a measured end inspiratory pressure. Inanother embodiment, a family of different pressure profiles is utilizedby the ventilator in the determination operation 502 to determine thepressure profile. The family of different pressure profiles is based ona set of received predetermined criteria, such as EPFTP and exhalationtime. In an additional embodiment, the at least one received criterionutilized by the ventilator in the determination operation 502 is atleast one parameter, such as a ventilation or patient parameter, that isrepeatedly measured to optimize the pressure profile. For example, theventilator in the determination operation 502 may repeatedly measure thetime it takes the patient to exhale the delivered amount of inspiratorygas to optimize the pressure profile. The ventilator in thedetermination operation 502 may utilize any suitable means fordetermining the shortest time to expire the delivered amount ofinspiratory gas and/or for determining the faster rate of lung emptyingbased on a received at least one criterion.

In some embodiments, the received at least one criterion is the pressureat the patient wye-fitting or the trajectory of the pressure profile. Inone embodiment, the pressure at the patient wye-fitting or thetrajectory of the pressure profile is determined by the ventilator inthe determination operation 502 by utilizing the following equation:P _(y)(t)=PEEP+(EIP−PEEP)e ^(−αt).

In this equation, P_(y) is the pressure at the patient wye-fitting, PEEPis the set positive end exhalation pressure, EIP is the measured endinspiratory pressure, α is greater than zero and denotes the EPFTP, andt is the amount of time measured from the onset of exhalation phase.This equation illustrates an exponential decay from EIP to PEEP, withalpha being varied to create different trajectories. For example, alphamay be varied (e.g., 0.1, 0.2, 0.3, . . . ∞) and then optimized basedupon a predetermined parameter, such as the amount of time it takes thepatient to exhale 50% of an inspired volume.

In another embodiment, the at least one criterion utilized by theventilator in the determination operation 502 to determine the pressureprofile is a predetermined pressure profile. For example, thepredetermined pressure profile may have a fast initial decay in pressurefollowed by an increase in pressure to provide a shorter amount of timerequired to exhale the delivered amount of inspiratory gas asillustrated in FIG. 4 . In some embodiments, the determination operation502 is performed by an exhalation module, a pressure profile module,pneumatic system, and/or a ventilator controller.

The at least one criterion may be any suitable criterion for controllingor effecting the pressure profile to provide for a faster rate of lungemptying, such as a percent of inspired volume/elapsed time, a flow as afunction of delta P (estimated lung pressure and circuit pressure), anAutoPEEP, measurements of patient resistance and/or compliance, adiagnosis (e.g., chronic obstructive pulmonary disease), an innerdiameter of artificial airway, a type of patient interface (e.g., maskor tube), an ideal body weight, carbon dioxide levels in exhaled gasand/or blood, an end expiratory flow, a patient assessment ofcomfort/dyspnea, a percentage of volume exhaled within a given period oftime after the start of exhalation, a mean expiratory flow, a peakexpiratory flow, a time to exhale a predetermined percentage of inspiredvolume, a time to reach a predetermined level of expiratory flow, afunctional residual capacity (FRC), a ratio of functional residualcapacity to total lung capacity (FRC/TLC), a breath rate, a ratio ofinspiratory to expiratory time, a tidal volume, a forced expiratoryvolume in 1 second (FEV₁), an expiratory lung volume, and/or aninstantaneous level of flow.

The embodiments as discussed above for determining the pressure profilein the determination operation 502 by the ventilator may be utilizedalone or in various combinations.

Next, method 500 includes a selection operation 504. The ventilator inselection operation 504 selects a pressure profile from the at least onedetermined pressure profile. In one embodiment, the ventilator of method500 selects the pressure profile predicted to provide the shortestamount of time to expire the delivered amount of inspiratory gas and/orto provide the fastest rate of lung emptying based the received at leastone criterion. In an alternative embodiment, the operator selects apressure profile from the at least one determined pressure profile.

As discussed above, the ventilator may utilize various different methodsto determine different pressure profiles. For example, the ventilatormay utilize different criteria to determine different pressure profilesfor faster lung emptying. In this embodiment, the ventilator mayautomatically select the pressure profile calculated based on a specificpredetermined criteria, such as such as a measurement of patientcompliance and/or resistance, and only utilize the other calculatedpressure profiles if a predetermined threshold is met by other measuredpatient or ventilator parameters. If the threshold is met in thisembodiment, the ventilator may automatically select a pressure profiledetermined based on exhalation time. In some embodiments, the ventilatormay have a stored predetermined nonlinear pressure profile, such as theone displayed in FIG. 4 , in addition to a calculated pressure profile.In this embodiment, the ventilator may automatically select thecalculated pressure profile unless a predetermined threshold is met bypatient or ventilator measured parameters. For example, thepredetermined threshold may be related to work of breathing or arterialblood gas saturation. The selection parameters listed above are merelyexemplary. The ventilator may utilize any suitable means for selecting apressure profile from a family of pressure profiles as would be known bya person of skill in the art for ventilating a patient.

In some embodiments, the family of pressure profiles is createdutilizing the following equation:P _(y)(t)=PEEP+(EIP−PEEP)e ^(−αt)which is described in detail above. In this embodiment, different valuesfor alpha ranging from 0.1 to 100 and/or to infinity may be applied overa time period to generate several different pressure profiles. Theventilator may select one of these calculated pressure profilesutilizing various different techniques. For example, the ventilator maycompare the calculated pressure profiles to previously deliveredpressure profiles and choose the calculated pressure profile closest toa previously utilized pressure profile that obtained the fastest rate oflung emptying. In another embodiment, the ventilator delivers adifferent calculated exhalation profile in each breath for at least twoconsecutive breaths. The ventilator in this scenario may then selectwhich pressure profile to deliver based on a predetermined parameter,such as the amount of time it takes the patient to exhale 50% of aninspired volume, which was measured during the delivery of the pressureprofile.

For example, a pressure profile with an alpha of 1 may be delivered in afirst breath and a pressure profile with an alpha of 2 may be deliveredin a second breath. During the delivery of these pressure profiles theventilator may measure the amount of time it takes a patient to exhale90% of the volume of an inspired breath. In this example, the ventilatorcompares each of these measured times and then delivers in the nextexhalation the pressure profile that results in the shortest measuredtime.

Next, method 500 includes a control operation 506. The ventilator incontrol operation 506 controls airway pressure and/or flow based on theselected pressure profile during the exhalation by the patient. Theventilator in control operation 506 delivers the airway pressure and/orflow based on the selected pressure profile by modifying valve settingsand/or flow rates during exhalation. In some embodiments, the controloperation 506 is performed by an exhalation module, a parameters module,pneumatic system, and/or a ventilator controller.

Method 500 may also include an inspiration operation. In the inspirationoperation, the ventilator delivers a volume of gas to the patient forinspiration during ventilation on the ventilator. The exhalation by thepatient includes exhaling the volume of gas inhaled by the patient fromthe volume of delivered gas.

In one embodiment, method 500 is performed by the systems illustrated inFIGS. 1 and 2 , which are described above.

In some embodiments, a microprocessor-based ventilator that accesses acomputer-readable medium having computer-executable instructions forperforming the method of controlling exhalation during ventilation of apatient is disclosed. This method includes repeatedly performing thesteps disclosed in method 500 and as illustrated in FIG. 5 .

In some embodiments, a ventilator system that includes: means fordetermining at least one determined pressure profile based on at leastone received criterion for an exhalation by a patient being ventilatedon a ventilator; means for selecting a pressure profile for delivery tothe patient from the at least one determined pressure profile; and meansfor controlling airway pressure and/or flow based on the selectedpressure profile during the exhalation by the patient.

FIG. 6 illustrates an embodiment of a method 600 for optimizingexhalation during ventilation of a patient on a ventilator. Asillustrated, method 600 includes a delivery operation 602. Theventilator in delivery operation 602 delivers airway pressure and/orflow based on a pressure profile during an exhalation to a patientduring ventilation on a ventilator. The pressure profile deliveredduring exhalation may be any suitable exhalation pressure profile. Theventilator either delivers pressure in accordance with a user-determinedpressure profile or a ventilator-determined pressure profile. In someembodiments, the ventilator utilizes a nonlinear relationship betweenairway resistance to the lung and airway pressure to determine thepressure profile. In some embodiments, the ventilator utilizes areceived at least one criterion to determine the pressure profile.

Next, method 600 includes a monitor operation 604. In the monitoroperation 604, the ventilator monitors at least one parameter during theexhalation by the patient. The at least one parameter may be anysuitable ventilator or patient parameter for determining a pressureprofile for providing faster lung emptying. For example, the monitors atleast one parameter may include ventilation data, data relating to anonlinear relationship between airway resistance and lung and airwaypressure, data relating to pressure profile trajectory equations, and/ormeasured/derived patient parameters. For example, the ventilator in themonitor operation 604 may monitor an exhalation time based on the amountof time it takes the patient to exhale at least a portion of gasinspired by the patient.

The monitor operation 604 may also include storing or calculating apressure, flow and/or volume profile that describes the exhalation ofthe patient. Such a profile may be stored as a series of measuredpatient parameters taken during the exhalation phase. The ventilator mayalso or instead perform one or more mathematical analyses on themeasured data in order to create a mathematical or model description ofone or more parameter profiles during the exhalation phase.

Further, method 600 includes a modify operation 606. The ventilator inthe modify operation 606 modifies the pressure profile based at least inpart on the at least one monitored parameter in order to increase therate of lung emptying and/or decrease the amount of time it takes thepatient to exhale an inspired volume. Additionally, in order to increasethe rate of lung emptying and/or to decrease exhalation time, theventilator in the modify operation 606 may further adjust a number ofother criteria, such as gas flow, ventilation modes, exhalation time,etc. However, the ventilator during the modify operation 606 does notadjust a received PEEP in the modified pressure profile. If a PEEP wasreceived by the ventilator, the ventilator in the modify operation 606maintains the received PEEP. For example, if the ventilator does notreceive a PEEP, the ventilator during the modify operation 606provides/determines a modified pressure profile with no PEEP. In someembodiments, the pressure profile is determined based on monitoredparameters from a group of previously delivered exhalations. Anysuitable pressure profile for shortening the amount of time to exhalethe delivered amount of inspiratory gas or that increases the rate oflung emptying during exhalation may be utilized by the ventilator duringmethod 600. For example, any suitable method for determining thepressure profile for method 600 as would be known by a person of skillin the art as described above in method 500 may be utilized by method600.

Next, the ventilator during method 600 either continues with or repeatsdelivery operation 602. Again, the ventilator during delivery operation602 delivers airway pressure and/or flow based on a pressure profileduring an exhalation to a patient during ventilation on a ventilator.However, during this delivery operation 602, the ventilator delivers amodified airway pressure and/or a modified flow based on the modifiedpressure profile to the patient during the current and/or nextexhalation. The current exhalation is the exhalation during which thereceived at least one parameter was monitored and utilized to calculatethe modified pressure profile. The next exhalation is the exhalationsubsequent to an exhalation where the received at least one parameterwas monitored and utilized to calculate the modified pressure profile.The next exhalation may further include every exhalation, apredetermined number of exhalations, or the number of exhalationsperformed in a predetermined amount of time subsequent to the exhalationwhere the at least one criterion was monitored or subsequent to thecurrent exhalation. Accordingly, the delivery of airway pressure and/orflow based on this modified pressure profile should reduce the amount oftime required by the patient to exhale the delivered volume of gasinspired by the patient and/or should increase the rate of lung emptyingduring the current and/or next exhalation.

In some embodiments, the ventilator may repeat method 600 for everybreath, after a predetermined number of breaths, or after apredetermined amount of time expires. In other embodiments, method 600is performed by the systems illustrated in FIGS. 1 and 2 , which aredescribed above.

In some embodiments, a microprocessor-based ventilator that accesses acomputer-readable medium having computer-executable instructions forperforming the method of controlling exhalation during ventilation of apatient is disclosed. This method includes repeatedly performing thesteps disclosed in method 600 and as illustrated in FIG. 6 .

In other embodiments, a ventilator system that includes: means fordelivering at least one of airway pressure and flow based on a pressureprofile during a current exhalation to a patient during ventilation on aventilator; means for monitoring at least one parameter during thecurrent exhalation by the patient; means for modifying the pressureprofile based at least in part on the monitored at least one parameter;and means for delivering at least one of a modified airway pressure anda modified flow based on the modified pressure profile to the patientduring at least one of the current exhalation and the next exhalation.Further, the modified pressure profile maintains a received PEEP.

Example 1

During testing with various simulation tools, it was discovered thatthis nonlinear relationship between airway resistance of the internallung with lung and airway pressure causes the exhalation lung flow todecay more rapidly than normal, thereby, preventing complete lungemptying when utilizing a pressure profile based on the assumption thatachieving the highest pressure gradient across the flow restrictionpromotes the greatest lung flow at any point in time, and the fastestrate of lung emptying.

For example, during simulation, the time it takes for 50% of theinspired tidal volume to be exhaled by the patient increases as theexhalation pressure decay is reduced (or as the EPFTP increases) andtarget PEEP is increased, as illustrated by FIG. 7 . FIG. 7 illustratesa graph of the effect of different patient's tubing exhalation pressureprofiles on the time required to passively exhale 50% of a giveninspired tidal volume in simulations.

For example, during simulation, the time it takes for 90% of theinspired tidal volume to be exhaled by the patient is reduced byreducing the rate of exhalation pressure decay (or increasing the EPFTP)and reducing the PEEP level, as illustrated in FIG. 8 . FIG. 8illustrates a graph of the effect of different patient's tubingexhalation pressure profiles on the time required to passively exhale90% of a given inspired tidal volume in simulations. Further, FIG. 8also illustrates that these changes affect the pressure profileperformance non-monotonically.

Accordingly, these results show that decreasing pressure as fast aspossible to the set PEEP rate does not always provide for the fastestexhalation. Further, these results show that a nonlinear relationshipbetween airway resistance and lung and airway pressure exists within thelungs.

Those skilled in the art will recognize that the methods and systems ofthe present disclosure may be implemented in many manners and as suchare not to be limited by the foregoing exemplary embodiments andexamples. In other words, functional elements being performed by asingle or multiple components, in various combinations of hardware andsoftware or firmware, and individual functions, can be distributed amongsoftware applications at either the client or server level or both. Inthis regard, any number of the features of the different embodimentsdescribed herein may be combined into single or multiple embodiments,and alternate embodiments having fewer than or more than all of thefeatures herein described are possible. Functionality may also be, inwhole or in part, distributed among multiple components, in manners nowknown or to become known. Thus, myriad software/hardware/firmwarecombinations are possible in achieving the functions, features,interfaces and preferences described herein. Moreover, the scope of thepresent disclosure covers conventionally known manners for carrying outthe described features and functions and interfaces, and thosevariations and modifications that may be made to the hardware orsoftware or firmware components described herein as would be understoodby those skilled in the art now and hereafter.

Numerous other changes may be made which will readily suggest themselvesto those skilled in the art and which are encompassed in the spirit ofthe disclosure and as defined in the appended claims. While variousembodiments have been described for purposes of this disclosure, variouschanges and modifications may be made which are well within the scope ofthe present invention. Numerous other changes may be made which willreadily suggest themselves to those skilled in the art and which areencompassed in the spirit of the disclosure and as defined in theappended claims.

What is claimed is:
 1. A method for controlling an exhalation phaseduring ventilation of a patient on a ventilator, the method comprising:determining, by a ventilator, a pressure profile for a future exhalationphase, the pressure profile causing a decrease in an exhalation time ofthe future exhalation phase relative to a previous exhalation phase ofthe patient; selecting the pressure profile for delivery to the patient;and based on the selected pressure profile, controlling, by theventilator, at least one of airway pressure and flow during the futureexhalation phase.
 2. The method of claim 1, wherein determining thepressure profile is based on at least one criterion.
 3. The method ofclaim 2, wherein the at least one criterion is a nonlinear relationshipbetween airway resistance and lung pressure and the airway pressure. 4.The method of claim 2, wherein the at least one criterion is anexhalation pressure fall time parameter.
 5. The method of claim 2,wherein the at least one criterion is an actual rate of pressure decay.6. The method of claim 5, wherein the actual rate of pressure decay isdefined by an exhalation pressure fall time parameter.
 7. The method ofclaim 2, wherein the at least one criterion is an amount of time thatthe patient takes to exhale a delivered volume of gas inspired by thepatient.
 8. The method of claim 2, wherein the at least one criterion isa measured end inspiratory pressure.
 9. The method of claim 2, whereinthe at least one criterion is a trajectory for the pressure profilecalculated with an equation of p_(y)=PEEP+(EIP−PEEP)e^(−αt), wherein theα is greater than zero and denotes an exhalation fall time parameter,wherein the PEEP is a set positive end-expiratory pressure (PEEP),wherein the EIP is a measured end expiratory pressure, wherein the t isan exhalation time, and wherein the P_(y) is a pressure at awye-fitting.
 10. The method of claim 2, wherein the at least onecriterion is a predetermined pressure profile that comprises: allowingpressure to fall below a set PEEP by a predetermined amount; increasingthe pressure after the pressure falls below the set PEEP to anotherpressure above the set PEEP by a set amount; and subsequently allowingthe another pressure above the set PEEP to fall to the set PEEP at apredetermined rate.
 11. The method of claim 1, wherein the pressureprofile for the exhalation is associated with complete lung emptying.12. The method of claim 11, wherein determining the pressure profile isfurther based on a received PEEP.
 13. The method of claim 12, furthercomprising: delivering a volume of gas to the patient for inspirationduring ventilation on the ventilator, wherein the exhalation by thepatient includes exhaling at least 90% of the volume of gas delivered tothe patient that was inspired by the patient.
 14. A medical ventilatorcomprising: a display; a processor; and memory storing instructionsthat, when executed by the processor, cause the ventilator to perform aset of operations comprising: delivering at least one of airway pressureand flow based on a pressure profile during a current exhalation to apatient during ventilation on the ventilator; modifying the pressureprofile for a future exhalation based on a non-linear relationshipbetween an airway resistance, a lung pressure, and an airway pressure toform a modified pressure profile, wherein the modified pressure profilemaintains a received PEEP; and based on the modified pressure profile,delivering at least one of a modified airway pressure and a modifiedflow to the patient during the future exhalation, wherein the modifiedpressure profile provides a decrease in an amount of time the patienttakes to passively expire an inspired volume of gas for the futureexhalation than a previous amount of time required by the patient topassively expire the inspired volume of gas during the currentexhalation.
 15. The medical ventilator of claim 14, the set ofoperations further comprising: monitoring at least one parameter duringthe current exhalation by the patient, wherein the at least oneparameter is at least one of: a time to exhale a predeterminedpercentage of the inspired volume; a percent of the inspired volume orthe elapsed time; and a force expiratory volume in 1 second (FEV₁). 16.The medical ventilator of claim 15, wherein the modified pressureprofile is further based on the at least one parameter.
 17. The medicalventilator of claim 14, wherein the non-linear relationship is modeledbased on a lung resistance equaling a nonlinear function between a firstamount of a first pressure in an upper airways compartment of a lung anda second amount of a second pressure in a lower airways compartment ofthe lung.
 18. The medical ventilator of claim 14, wherein a trajectoryof the modified pressure profile is an exponential decay from EIP toPEEP.
 19. The medical ventilator of claim 14, wherein the modifiedpressure profile further provides a decrease in an amount of time thepatient takes to passively expire 90% of an inspired volume of gas thana previous amount of time required by the patient to passively expire90% of the inspired volume of gas.
 20. A medical ventilator comprising:a display; a processor; and memory storing instructions that, whenexecuted by the processor, cause the ventilator to perform a set ofoperations comprising: determining, with a ventilator, a pressureprofile for a future exhalation phase, the pressure profile causing adecrease in an exhalation time of the future exhalation phase relativeto a previous exhalation phase of a patient; selecting the pressureprofile for delivery to the patient; and based on the selected pressureprofile, controlling, with the ventilator, at least one of airwaypressure and flow during the future exhalation phase.